The development of blood vessels is a major event in kidney morphogenesis, however, the molecular basis of kidney vascularization is unknown. A role for soluble angiogenic factors has been postulated.. Vascular endothelial growth factor (VEGF) is the best candidate for such a role because it is a secreted direct acting endothelial cell mitogen required for vasculogenesis. The hypotheses to be tested are: 1) VEGF mediates glomerular vascularization, and 2) hypoxia regulates VEGF-mediated angiogenesis. To address the first question, we will define the effect of VEGF on kidney organ culture and we will identify VEGF target cells using VEGF receptors antibodies and beta-gal staining of FIK-1(+/-) transgenic explants. To test the second hypothesis, cultured kidneys will be exposed to hypoxia and endothelial cell differentiation and proliferation will be assessed by morphologic studies. VEGF role mediating these events will be defined using anti-VEGF neutralizing antibodies. These experiments will be performed using fetal rats and FIK-1(+/-)transgenic mice. We will identify and clone transcription factors involved in VEGF regulation by hypoxia using an expression library constructed ad hoc from hypoxic kidneys, screened with O2 sensitive DNA probes and differential display PCR amplification of mRNAs from hypoxic and control explants. The combination of histochemical, molecular biology and transgenic technology will enable us to determine the origin of renal endothelial cells and to define the role of VEGF in kidney vascularization. Understanding the molecular mechanisms governing vasculogenesis and angiogenesis should generate new strategies for prevention, diagnosis and treatment of renovascular disease and cancer.